1. Field of the Invention
The present invention relates to a low permittivity composite material having improved electric characteristics and other properties based on dispersing hollow fluoro-resin particles in a base material comprising polymer material. 2. Brief Description of the Background of the Invention Including Prior Art
Various types of plastic and rubber have been in use as insulating material for a long time. It has recently been proposed, in Japanese Patent Applications Laid Open No. 62-48710 and No. 62-48711, to mix microscopic, hollow balls of glass or silica, having included nitrogen gas, carbonic acid gas, or some other gas, as a filler, with an insulating material with the aim to improve the electrical characteristics and properties of the insulating material by the use of these low permittivity fillers.
Since these microscopic hollow balls are hard based on their chemical composition, their nature, and the properties of these materials, the softness of the resulting insulating material is substantially reduced as compared with the base material after the mixing of the soft insulating material with the hollow balls. The resultant fragility of the composite material presents a serious problem.
It is also conceivable to use microscopic hollow balls of plastic instead of glass ones. Nevertheless, the use of microscopic hollow balls made of a plastic material gives rise to another problem. The conventional method of manufacturing microscopic hollow balls depends heavily on properties related to a molding process, such as the fusing viscosity, melting point, flow and space filling properties, etc. of the resin which serves as the base material. Therefore, a material such as a fluoro-resin which, despite its excellent properties as a hollow ball material, exhibits inadequate processing properties for molding, and will present difficulties if it has to be used as a resin material for hollow particles.
Accordingly, those materials available for molding hollow particles are made of a very limited number of materials including vinylidene chloride-acrylonitrile copolymer. Nevertheless, there remains a problem in heat resistance due to a low melting point for microscopic hollow balls made of vinylidene chloride-acrylonitrile copolymer. Another drawback of vinylidene chloride-acrylonitrile copolymer is that it is easily affected by organic solvents. Therefore, vinylidene chloride-acrylonitrile copolymer imposes many restrictions on a manufacturing process and requires specific conditions for its subsequent use when mixed with an insulating material such as plastic. Thus, substantial problems remain associated with a conventional composite material and its manufacture involving use of microscopic hollow balls made of glass or plastic.